1. Field of the Invention
The present invention relates to leads which are electrically conductive and which are suitable to be implanted in a human or animal body. Such leads may for example be used to conduct electrical stimulation pulses from an implanted heart stimulating device to the heart of said human or animal body. Leads may, however, also be used in connection with other kinds of medical devices. Preferably the heart electrode leads are adapted to be insertable via the vascular system into the human or animal heart. Such heart electrode leads are particularly suitable for intracardial stimulation of the heart with the help of an implantable pacemaker or defibrillator. The invention concerns both a lead as such and a method of producing a lead.
2. Description of the Prior Art
A large number of different leads are known in the art. A lead normally has a proximal end portion to be connected to a device, for example a heart-stimulating device, and a distal end portion that is to be positioned at a predetermined position in the body, usually in or at the heart. A heart electrode lead may be unipolar or bipolar. A unipolar lead has only one single electrode member usually arranged at the tip of the distal end portion of the lead. A bipolar lead has two electric poles. Also this kind of electrode lead usually has one electrode member located at the tip at the distal end portion of the lead. The lead has at least one electric conductor, which extends from the proximal end portion to the electrode member at the distal end portion.
For example in the case of a lead for a heart stimulating device, it is known that when a lead has been implanted into or at the heart, the stimulation threshold is higher during a certain time after the implantation and then becomes lower. It is also known that this stimulation threshold may be lowered by providing a drug, such as a steroid, at the distal end portion of the lead. The drug is arranged such that it will be dispensed to the surrounding body tissue over a period of time.
U.S. Pat. No. 5,103,837 describes the use of a coating including a drug [is provided] on an electrode member of titanium nitride.
U.S. Pat. No. 4,819,661 describes different leads with helical fixation members. A drug impregnated matrix, preferably of a biocompatible silicon adhesive, is positioned in a cavity at the distal end portion of the lead.
U.S. Pat. No. 5,003,992 also describes a lead with a helical fixation member. A plug made of a polymer with a drug is located in a cavity at the distal end portion of the lead.
U.S. Pat. No. 5,002,007 discloses a lead with a helical fixation member. A cylindrical plug fabricated of a silicon-based polymer incorporating an anti-inflammatory drug is positioned in a cavity at the distal end portion of the lead. The fixation helix may also be provided with a groove along which the drug may be released.
U.S. Pat. No. 4,972,848 describes a lead with a helical fixation means. A release device made of a polymer and incorporating a drug is provided in a cavity at the distal end portion of the lead,
U.S. Pat. No. 4,506,680 describes a sintered metal electrode member located at the distal end of the lead. In a cavity inside of this electrode member a polymer impregnated with a drug is positioned.
U.S. Pat. No. 4,577,642 describes a lead with a porous sintered metal electrode member located at the distal end portion of the lead. In a cavity inside of the electrode member, a drug is retained in a solid plug or a powder wherein the drug is compounded with an appropriate molecular sieve material.
U.S. Pat. No. 6,038,482 discloses a lead with an electrode member positioned at the distal end portion of the lead. The electrode member has an interior cavity and a bore extending between the interior cavity and the exterior surface of the electrode member. A matrix member with a drug is positioned in the interior cavity. The exterior surface of the electrode member is coated with a wetting agent with the same drug as in the matrix. Also the bore is filled with a wetting agent with the same drug as in the matrix. According to this document, a tiered delivery of the drug is achieved, where the drug on the exterior surface and in the bore elutes within approximately a 24 hour period and the drug in the matrix elutes for a much longer term measured in months or years.
U.S. Pat. No. 4,819,612 describes a cardiac pacing lead that includes a porous element tip electrode that can be loaded with a drug that will be eluted upon implantation. One or several matrices can be housed in a recess behind the tip electrode for continuous drug elution.
European Application 334 306 describes a transdermal adhesive for diminishing release of active substances.